1. Field of the Invention
The present invention relates to a test method for image, particularly to a fast and high-correctness test method for image sharpness.
2. Description of the Related Art
With the advance of electronic industries, many digital video devices have emerged, such as digital cameras, digital video cameras, and mobile phones with a digital camera. As to digital cameras, the user can check the captured pictures in situ or anytime later from the attached LCD viewer of a digital camera; further, a digital camera directly records an image by digital data, which makes the processing and storage of the pictures more convenient; besides, the size of a digital camera is much smaller than that of a conventional camera, and thus, the portability of a digital camera is also much better than that of a conventional camera. Therefore, the market share of digital cameras has exceeded that of the conventional cameras.
Owing to the progress of optoelectronics, the image quality of a digital camera has been greatly promoted from several hundred thousand pixels to more than twelve million pixels. Even magnified many times, such a high-pixel image can still maintain its definition. When the user takes a picture, there is usually a vibration transmitted from the hand to the digital camera. Even though the vibration during taking a picture is very slight, the captured image may still be blurred. When viewed in situ, such an image, which is display on the LCD viewer of the digital camera, may seem sharp because the size of a common LCD viewer is usually small and less than 3.5 in. However, the image will appear indistinct when it is displayed in a large-size LCD or printed on a photo paper, i.e. observed in magnification. Thus, the LCD viewer of a digital camera may not always present the real status of an image. Usually, the user does not perceive such a fact until the image is processed in a computer or printed on a photo paper.
To solve the abovementioned problem, Microsoft Corporation proposed a test method for image unsharpness (U.S. Pat. No. 6,548,8000), wherein multiple images are analyzed with an identical edge parameter to determine the unsharpness thereof. However, in such a method, each image needs multiple pantograph operations, which needs a big memory and a lot of calculation time. Further, the test results are not so good as expected. Therefore, how to develop a fast and effective image-sharpness test method has become one of the problems the industry must overcome.
Accordingly, the present invention proposes a test method for image sharpness, which can fast and correctly test image sharpness, to overcome the abovementioned problems.